Moller



R. MULLER 2,735,364 OFFSET PRINTING PROCESS AND MECHANISM THEREFOR Feb.21, 1956 Filed March 4, 1952 IN VE N TOR RUDOLF MULLER A T TORN UnitedStates Patent OFFSET PRINTING PROCESS AND MECHANISM THEREFOR RudolfMiiller, Mutterstadt-Pfalz, Germany Application March 4, 1952, SerialNo. 274,690 Claims priority, application Germany March 7, 1951 6 Claims.(Cl. 101-142) The present invention relates to ofl set printing. Moreparticularly it relates to new offset printing processes practicedwithout expressly adding water or fountain solution to printing platesof the type which are provided with ink receptive images that are waterrepelling, the non image areas of the plate being hygroscopic or waterreceptive and ink repelling in use. The invention also relates to newprinting machines for carrying out the new process.

In offset printing, the printing plate is made wet usually by means of asystem of dampening rollers which are continuously supplied with wateror a fountain solution containing various beneficial agents in additionto water. The regulation of the supply of water or fountain solution andthereby the degree of dampening of the plate requires a great deal ofexperience. Insufiicient water may permit the background areas to takeup ink or scum up and too much water may interfere with the transfer ofink and cause the print to look gray instead of black. When the machineremains idle, the plate gets dry rapidly and oxidation takes place whichmay also result in toning or scumming of the non-image areas of theplate.

It has also been proposed to supply the moisture required on theprinting plate by cooling the surface of the plate to a temperaturebelow the dew point of the air by means of a refrigerating machine sothat moisture will condense from the air onto the surface of themachine. However, in using this process with motor-driven printingmachines, it has been found that ordinarily sufiicient moisture is notobtained by merely cooling the plate to The apparatus is renderedexpensive and uneconomical by such additional equipment. Furthermore, incontinuous operation, the printing plate became cold enough to raise theconsistency or viscosity of the printing ink on the offset cylinder tosuch an extent that the ink would no longer transfer perfectly and theprints would be unusable. This effect also severely limited thetemperature difference between the plate and the atmosphere which couldbe used to increase the amount of moisture on the plate.

Whether moisture is applied to the plate by cooling or by means ofrollers, it is undesirable for the moisture to transfer to the olfsetcylinder When too much moisture gets on the offset cylinder the printstend to be gray rather than black and the image areas may bediscontinuous, or in severe cases, lines may be broken.

The objects of the present invention are to provide printing processesand machines using the principle of cooling the plate to obtain moisturethereon without the use of transfer rollers or the like, in which theplate may be cooled to lower temperatures than in previous processes andmachines but in which the ink remains of the proper consistency andreadily transferable and in which the offest cylinder remains completelyfree of moisture which makes it practical to print on coated papers,sheets of regenerill ated cellulose and even glass which has beenconsidered very difficult until now.

In the new printing process, the support for the print ing plate and theplate itself can be cooled by means of a refrigerating machine totemperatures far below the dew point temperature of the air and evenbelow 0 C.; i. e. below freezing, in case that a so far reaching coolingof the plate proves necessary with respect to the actual prevailingconditions of temperature and humidity. A difference of 5 to 10 degreesbetween the dew point temperature and the temperature of the surface ofthe printing plate has proved to be advantageous. In case that coolingbelow 0 C. is realized, the surfaces of the support and of the printingplate itself are covered with an antifreeze agent to prevent icing. Theuse of the antifreeze agent between the support and the printing platealso increases the rate of heat flow from the plate to the support sothat the cooling is more efficient. Since most antifreeze agents arealso hygroscopic, they also tend to help draw moisture to the plate. Itis also useful to select antifreeze agents which act as antitoningagents or antiscumming agents or a combination of antifreeze agents maybe used. Suitable antifreeze agents are glycerine, ethylene glycol andother polyvalent aliphatic hydroxyl compounds. Acids and gums may alsobe applied to the plate in combination with the antifreeze agent.

Another important feature of the invention is to heat the offsetcylinder and possibly also the inking rollers. This prevents the inkfrom getting too stiff and also keeps the offset cylinder free ofmoisture for reasons discussed above. Since the surface of the offsetroller is the important part to heat, it is preferred to heat by thermalon the roller surface by said heating will be sufficient for thevaporization of undesired moisture on the rubber blanket.

The invention will be more fully understood by reference to thefollowing description taken in connection with the accompanying drawingsin which:

Figure I is a diagrammatic view in elevation of a fiat bed offsetprinting press constructed according to the invention.

Figure II is a diagrammatic view in elevation of a rotary offsetprinting press constructed according to the invention.

Figure I shows a hand operated machine, although it will be appreciatedthat the invention can also be readily used in an automatic machine ofthe same type. In Figure I, the printing plate 2 is secured to the flatbed support 4 by conventional means. The material to be printed on 6 iscarried on the platform 8. The platform 8 may be provided with heightadjustment means such as the wing nut 10 counteracted by the springs 12in order to enable adjustment for a stack of sheets for example. Theoffset cylinder 14 may be pulled over the printing plate 2 and over thematerial 6 by the handle 16 picking up an ink image from the plate 2 andtransferring it to the material 6. The inking rollers 18 which may be ofconventional design are pulled after the offset cylinder 14 by means ofthe link 20 and apply ink to the plate 2 for the next printing cycle.

The refrigerating machine 22 which may be of the conventional householdtype is provided for cooling the support 4 and the printing plate 2. Therefrigerating machine 22 includes a com ressor 24 forcing therefrigprinting surface of the plate 2. The refrigerating fluid havingabsorbed heat from the support 4 is returned to the heat radiator 28which is cooled by means of a fan 30. The fan 30 may be driven by thesame electric motor 32 as is used to drive the compressor 24.

The thermal radiation unit 34 is provided over the offset cylinder 14 toradiate heat to the surface of the rubber blanket thereon. The amount ofheat radiated to the offset cylinder is suflicient to keep the cylinderfree of moisture and to keep the ink of proper consistency. The thermalradiation unit 34 may consist of a resistance unit 36 and a heatreflector 38 which may have a concave reflecting surface as shown fordirecting the heat rays at the offset cylinder 14. It will beappreciated that as the inking rollers 18 pass under the thermalradiation unit 34 they will also be heated thereby. If more heating ofthe inking rollers is desired, the thermal radiation unit may beextended to cover the inking rollers at the end of the stroke or if itis desired to heat only the offset cylinder, the thermal radiation unitmay be carried on the side supports for the offset cylinder so that itmoves back and forth therewith.

In the rotary offest press shown schematically in Figure II, as is wellknown in the art, the support for the printing plate 43 is in the formof a plate cylinder 42. The machine is also provided with an offsetcylinder 44 and the pressure cylinder 46. The plate cylinder 42 isprovided with suitable means for holding a printing plate 43 usually offlexible material so that the image surface coincides with thecircumference of the cylinder. The plate cylinder is provided withcooling means which may be a refrigerating machine similar to that showndiagrammatically in Fig. I. In this case, the expansion cooling coil 48is provided in a position within the cylinder 42 so it can absorb heattherefrom. The, cooling of the Plate cylinder 42 also results in coolingof the printing plate 43 so as to condense moisture on the surfacethereof. Ink is applied to the surface of the printing plate 43 by meansof the inking rollers 50. In the usual manner, the condensed moisturewill cling to the non-image areas of the printing plate 43 repelling theink while the, image areas will accept the ink from the inking rollers50. An antifreeze agent is applied to the surface of the printing plate43 and also between the plate and the plate cylinder 42 for the samereasons as it is applied to the machine shown in Fig. I.

The ink from the image areas of the printing plate 43 is transferred tothe rubber blanket 52 provided at the circumference of the offsetcylinder 44. A thermal radiation unit 54 is provided to direct heat atthe surface of the rubber blanket 52 to keep it free of moisture and tokeep the ink of the proper fluidity. The material 56 to be printed isfed by means known in the art between the cylinders 44 and 46. Thefunction of the cylinder 46 is to hold the material in contact with theoffset cylinder 44 so that the ink is transferred thereto forming theprints 58. Means may also be provided to heat the inking rollers inorder to keep the ink fluid thereon.

In another type of offset printing machine known in the art only twocylinders are provided, one of which has twice the circumference of theother. The smaller cylinder is the offset cylinder and the printingplate is carried around one half the circumference of the largercylinder. The other half of the larger cylinder acts as a pressurecylinder when the image is transferred from the smaller offset cylinderto the base material for the prints. It will be understood that theinvention may also be applied to this type of printing machine bycooling the plate portion of the large cylinder and heating the smalleroffset cylinder.

By treating the surfaces of the flat bed support or plate cylinder andthe surface of the printing plate with. an.

antifreeze agent, it is possible to maintain. their temper= ature farbelow C. Thus it is possible to. produce a great difference between thesurface temperature of the printing plate and the dew-point temperatureof the air so that an adequate quantity of water will be precipitatedonto the plate from the air for all normal temperatures and humidities.

The thermal radiation striking the surface of the offset cylinder bringsabout a sudden rise in the temperature of the outside surface includingthe greasy ink film image covering the rubber blanket, due to the factthat the mass of ink is very small and the heat conductivity of thegreasy ink and rubber blanket is low. This rapid rise in temperatureresults in the immediate vaporization of any moisture which may havetransferred from the printing plate to the offset cylinder. Theradiation method of heating is preferred to heating by means of hot airfor example because the latter method is likely to carry dust which willbe picked up by the greasy ink film.

When the new procedure is used the surface of the offset cylinder whichtouches the paper or other image receiving material is completely freeof moisture and the ink coming into contact with the paper is in ahighly fluid state so that it readily penetrates into the pores of thepaper forming deeply colored prints of high con trast. Perfect printscan also be obtained on glass because no moisture is present which wouldinterfere with the adhesion of the ink to the glass and the ink is in ahighly fluid condition so that continuous uniform images may betransferred.

It will be appreciated that the invention eliminates many disadvantageshitherto experienced in connection with the offset printing process andopens new fields to offset printing.

Having thus described the invention, what is claimed is:

1. In a mechanism for lithographing of the offset type comprising asupporting means for a printing plate, a printing plate supportedthereon having image and nonirnage areas, means for applying printingink to said plate,

means for cooling said supporting means to condense moisture on saidplate whereupon the moisture will cling to the non-image areas thereofand repel printing ink, the printing plate being cooled thereby to atemperature below the dew point of the atmosphere, an oflFset cylindercontaining means for transferring an inked image from the plate ontomaterial to be printed, means for heating the surface of said offsetcylinder to keep it free of moisture and maintain the inked imagethereon in an image transferable consistency, and a liquid water solublefreezing point depressant located on said printing plate.

2. The mechanism of claim 1 wherein the depressant is also located onthe surface between the supporting means and the printing plate.

3. In a mechanism for lithographing of the offset type comprising asupporting means for a printing plate, a printing plate supportedthereon having image andnonimage areas, means for applying printing inkto said plate, means for cooling said supporting means to condensemoisture. on said plate whereupon the moisture will cling to thenon-image areas thereof and repel printing ink, the printing plate beingcooled thereby to a temperaure below the dew point of the atmosphere, anoffset cylinder containing means for transferring an inked image fromthe plate onto material to be printed, a thermal radiation unit directedat the surface of said offset'cylinder to keep it free of moisture andmaintain the inked image thereon in an image transferable consistency,and a liquid water soluble freezing point depressant located on saidprinting plate.

4. The mechanism of claim 1 wherein the heating means is also arrangedto heat said ink applying means.

5.. The; process of offset printing comprising the steps of condensingmoisture on an inked printing plate, while simultaneously subjecting;the exposed surface of said plate to: a. liquid water soluble freezingpoint depressant, transferring. the inked image from said plate to thesurface of an ofiset cylinder, heating the offset cylinder surface tomaintain it free of moisture and the inked image thereon ReferencesCited in the file of this patent in a transferable consistency, andtransferring the inked UNITED STATES PATENTS image from the offsetcylinder surface to a preselected material to be printgd rnw ll Feb. 13,6. The process of offset printing comprising the steps 5 8973831Hergeshelmer P 1908 of condensing moisture on an inked printing plate by0001- 1,479,819 f 8, 1924 ing it While simultaneously subjecting theexposed sur- 210251046 Goedlke e 1935 face of said plate to a liquidWater soluble freezing point FOREIGN PATENTS de ressant whereby thetemperature of said late is maintaiiied below 0 C., transferring theinked irnage from 10 584240 Great Bmam 1947 said plate to the surface ofan offset cylinder, heating OTHER REFERENCES the offset cylinder surfaceto maintain it free of moisture and the inked image thereon in atransferable consistency, and transferring the inked image from theoffset cylinder surface to a preselected material to be printed. 15

Printing Inks, Carelton Ellis, Reinhold Publishing Corp., New York,1940, page 475.

